When I was young and single, I drove a 1973 Datsun 240Z with a 3 speed auto, 2.4L straight 6, twin Hitachi (SU) carbs.
It returned about 25 USmpg (30 imperial) general driving and about 29 USmpg (35 imperial) on a trip.
Naturally, the 5 speed manual was even better with the overdrive gear.
I emailed at the "Feedback" link at the bottom of any page on the site, and asked about my own Torino and some lady replied about 2 days later with a PDF file of the page containing my car. Very nice. I am not certain if they would provide older data in bulk, but it's worth a shot to ask, right?
Not many fuel economy stars before 1981 or so, but they are out there.